Telephone trunking system.



T. G. MARTIN.

TELEPHONE TRUNKING SYSTEM.

APPUCATION FILED DEC-2. 1910. RENEWED MAY 24,1918.

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' T. G. MARTIN. TELEPHONE TRUNKING SYSTEM.

APPUCATION FILED DEC-2,1910. RENEWED- MAY 24.1918.

Patented Jan. 14, 1919.

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' T; G. MARTIN.

TELEPHONE TRUNKING SYSTEM. YAPPLICATIOMHLVEDA DEC. '2, 1910'. RENEWED MAY 24 1918. 1,291,585.

I Patented Jan. 14, 1919.

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G l M mmmim T. G. MARTIN. TELEPHONE TRUNKING SYSTEM. APPLICATION F |LED 050.2. mofn'zuzwzp Min/24.1918. 1,2915% Patented Jan. 14;"1919' ISHEETSSHEET I.

WYT/VESSES UNITED sTA- Es PATENT OFFICE.

TALBOT c. MARTIN, or CHICAGO, ILLrNors', ASSIGNOR TO AUTOMATIC ELECTRIC COMPANY, 01 CHICAGO, ILLINoIs, A CORPORATION or ILLINoIs.

TELEPHONE TRUNKING SYSTEM.

Specification of Letters Patent.

Patented Jan. 14 1919.

Application filed December 2, 1910, Serial No. 595,237; Renewed May 24, 1918. Serial No. 236,411.

T 0 all whom it may concern:

Be it known that I, TALBOT G. MARTIN,

a citizen of the United States of America,

and resident of Chicago, Cook county, Illinois, have lnvente d a certain new and usetul Improvement lIl Telephone Trunking S toms, of which the following is a speci-.

ers are employed for automatically finding idle trunks and repeating calling impulses to the next switch.

My invention also relates to automatic or semi-automatic telephone exchange systems in which either three-wire or two-wire line circuits are employed, or both, in .which there are automatic switches that can be controlled over these circuits. By a three-wire system is meant one in which the line circuitis grounded to control the automatic switch, such as a selector or a connector, a common method being to ground first one side of the line and then the other tocause the switch to operate in accordance with some digit or digits of the called number. By a two wire system is meant one in which the switches are controlled over metallic line circuits-that is to say, by controllingthe two sides of a line circuit in series, and without grounding the line.

An obj ect of my invention is to provide an improved combined trunk selector and re-- peater, for use in a three-.wire system, having means for automatically controlling a ringing apparatus, the said ringing appara tus, as herein disclosed, being located in the connector by which'the called line is found, and the control of said apparatus being exercised by the means in said selector and re peatcr as soon as the operation of the connector is completed, the automatic and intermittent ringing operation continuing until the called party answers.

Another object of my invention is to provide an improved combined trunk selector and repeater, for use in a two-wire system, having means for repeating electrical impulses over the -two sides of the selected trunk in series-.that is to say, for control which the semi-automatic connection has been made. I

Another object is to provide an improved construction and arrangement whereby it is possible to call semi-automatically from a three-wire exchange to a two-wire exchange,

and from thesaid two-wire exchange to the said three-.wire exchange, with double supervision in each case.

It is also an object to provide certain details and features of improvement and general combinations tending to increase the efficiency-of a telephone exchange system of this particular character.

T the foregoing and other useful ends my invention consists in matters hereinafter set forth and claimed.

In the accompanying drawings Figures 1., 2, 3 and 4 taken together represent. a complete circuit connection between a calling substation A (Fig. 1) and a called substation A (Fig. 4) in a, system embodying the princlplesof my invention.

Figs-5 and 6 show additional apparatus by means of which a call may be extended from the substation A to substation A of said system. which apparatus is shown in the -alling substation over the two sides of 100 the line in series. Th'e'exchange to which the substation A belongs is of the so-called thirec-wire t vpc-that is, of the type in which the central office apparatus is controlled from the calling substation by 106 ground impulses transmitted over each side of the line separately.

In Fig. 1 there is shown a line switch C which is individual to the line of the substation A group of these line switches is controlled by 800111111011 mechanism'l), the

, principal"features of which are more fully v system. AtLun ordinal switch is shown. At (Fig-gs) 8. three wire connector is shown. The Substation! is provided with an individuallineswitch at the central office. This lineswitchlihs access to trunk lines which terminate in three-wire. selectors L,

shown in Fig. 7.. v station A there is also ameter or call-registering device E. All the line switches which are controlled by the master switch D have common access to a number of. selector switches F. 'Theseselectors have access to a number of trunk lines at least some of which lead to operators jachs J (Fig. 2). AUG,-

Fig. 2, there is shown an operators cord circult, which is the medium of c0nnection'be-} tween the two-wire and the three-wire 'ex-i ,p chen es. At-I, Fig. 3, there is shown p. com';

binet selector and repeater for' a three-wire lectors have access, to 'tru O is the connecting link between the threewire exchange and the two-Wirejcxchange.

.At- I",(Fi'g. 6): therei's represented a combined selectorsncl repeater for atwo-wire At M isrepresented efitwo-wire system;

connector.

In the various drcwin ing current generators a number of ringshown. A number of batteries B ere represented having one terminal grounded. There freed be but one battery,however, or preferebly' onebattery in each exchange.

he two-wire substation A comprises the usualreceiver 2, switch hook 3, transmitter 4, ringer 6 and condenser 7. Since it is an automatic substation, it is also provided with the impulse springs 8 and 9 and an impulse f wheel 10 which carries upon its periphery a number or impulse teeth 11, and is secured to All a. shaft 13 to which there is also secured a dial (notshown') provided-with finger holes.

. The teeth 11 on the impulse wheel 10 are so o giiianged that as they are rotated forward to Gail any digit the springs 8 and 9 are not affeoted;.but when the impulse wheelis returned to normal position, then the springs 8 and 9 are separated by the teeth 11 EL number' oftiines corresponding to the digit culled. I

In the substation A (Fig. 4) the impulse wheellfi is provided with tense-called vert-ical impulse teeth 17 and one rotary impulse tooth 18. These teeth are so arranged that "as the impulse wheel is rotated forward through the medium of'the dial, the rotary toot-l1 i8 forces the sic-called rotary impulse spring 19 into engagement with the ground spring 21. As the wheel 16 returns to noru mal position the verticalimpulse springfQO isforced into engagement with the ground Allotted tot he line of subthree-wire se actor. v a "switch-l) ilre modified formsof the general 5;. Theseeesn I lines, some of. which lead to jacks J The operators cord.

and. Q andtbusy signaling 'Inachines "R, R and R are spring 21 a number of times, corresponding to the'digit called, after. which the rotary spring 19 is once moreforced into contact with sprin 21 by the tooth 18. While 11nv icing transmitted the connectionv pplses are tween the two sides of the l ne are broken betwernthp sprir'igs 22 and 23., which come into en" r moved the switch hook, but are per.-

-.|nt;when the receiver is re- (substation A, and the master ypes of line and master switches'disclosed n'jBritish-Patent-#26,301 of 1906, and in York,'-0f June 6, 1908., As herein represented, the line switch C comprises, among other details, a plunger 38 (Fig. 7) attached tofthe endof a, 'so called plunger arm 39 which, is controlled by the-magnet 40; The

magnet 40 also controls the relay HIYllfllltlTQS 41 and 42, and is composed of four windings, namely, a pull-in winding 43, a holding or cut-ofi wmding 44, line winding 46' and an auxiliarywinding 45. The core of the magnet is provided near thecenter of its length with a lateral projection 47, by means of which the magnet is mounted upon the bracket 48, upon which the armatures 39, Hand- 42. are pivoted. With this method 101 of mounting the magnet; the magnetic circuit of-the windings 43 and 4L4 is maintained separate from that of the. windings 45and lfi' so that 'tlie a rmatures on one end of the magnet are not affected by the lee en'ergization ofthe windings upon the other end. .Of the two windings upon the upper end of the magnetonly the winding 4-3 is strong'enough to attract the plunger arm 39 from its normal position. -Tll8 winding 11c 44 is'not strong enough to thus operate the plunger arm, but will hold it' in cooperated position after 1t has becn'd-rawn down by the Winding 43. When the plunger arm 39 isattracted by the magnet 40 the plunger of the switch is forced into a bank of contact springs, forcing springs 49, 51, 53 and 55 into engagement with-springs 50, 52, 54 and- 56, respectively.,,{ Although only one set of springs 49-5 6 is shoim, each line switch C is" provided with a number of such groups of springs, each group forming the termi nal'of a trunk line leading to a selector F. Each trunk line is multipled through the corresponding springs .of all the line switches of the group which is controlled by the master switch D. The'plungers of the line switches ofthis group normally engage the plunger shaft, 57 (Fig. 7), and through the medium of the master switch D are nor- 13c means of a link 61 in such a manner that arotary motion of the ratchet wheel is transmitted to the plunger shaft 57, imparting to it an oscillatory motion about the shaft (10. so as to move the idle pl-ungers back and forth in front oftheir trunk terminals. To

- the shaft there. is secured a locking plate 62 provided near its outer edge with a number of openings 63 which are adapted to be engaged-by thepin 6-1 upon the end of the armature of the relay 66. The openings in the plate 62 are so spaced that the pin ()4 can engage one of them only when the plungers that are in locking engagement with the plunger shaft are directly in front of the corresponding trunk terminah The master switch is also provided with a bank of contacts comprising a common segment and one individual segment II for each trunk to which the line switches have access. The wiper 29 always keeps the common segment in electrical connection with the individual segment corresponding to the trunk line before which the idle plungers are being held by the master switch.

The meter E is operated by a magnet 67, comprising two windings (i8 and (19, which is so adjusted that neither winding alonecan attract the armatureTO. but one windin can hold it in its operated position aftei it as once been attracted by both windings. The selector F is of the general type dis-' closed in United States Letters Patent #815,321, granted March 13, 1900, to Keith.-

' the vertical magnet 74 and a rotary motion controlled by the rotaryniagnet '75. The side switch comprising the wipers 76, 77, 78 and 79 is controlled by the private magnet 80 in the usual manner. The release magnet 81 is connected with the battery only when the switch shaft is raised one or more steps from its lowest "position. whereby the arm 82 permits the spring 83 to engage the spring 84. The shaft and side switch ofthe selector are restored to normal position immediately upon the energization of the release magnet rather than by its deenergization. as shown in said selector patent,

The relays 85, S6 and 87 deen'ergize slowly after their energizing circuits have been broken. This slow action may be ol'itained by securing a ring of copper or other conducting material around one end of the core.

The operators cord 0 (Fig. is si nilar to the usual type of cord circuit used in manual switchboard practice, the supervisory circuits being particularly adapted, however, to operate in the system disclosed herein. The cord is provided with a calling device which may be of any suitable character, but is represented diagrammatically by two push buttons 88 and 89.

The selectoi'i'epeatei' I combines the functions of a selector and a repeaterthat is,

it operates in response to one digit to select' an idle trunk out. of a particular group, corresponding to the digit called, and then operates in response to the following digits to repeat impulses over the selected trunk to the succeeding switches.

The three-wire connector M (Fig. 4)- is of the general type of connector disclosed in United States Letters Patent #815,176, granted March 13, 1906, to Keith, Erickson a Erickson, the circuits being modified somewhat in order operate in a common battery system.

manual switch board practice. It is provided with an automatic calling device represented by the two impulse springs-9O and 91.

The selector repeater I (Fig. 6) is like the selector repeater I, Fig. 3, in that it com biiies the features of a selector and repeater, but differs from it in that it is adapted to be controlled over the two sides of the call ing line in series. The connector Mv is also adapted to be controlled over the two sides of the line in series.

Having given a general description of the apparatus I will now explain in detail the operations by which a subscriber of one eX change can call a subscriber at the other exchange. It will first be explained how the subscriberat substation A can call substation A".

Upon the removal of the receiver at the substation A a circuit is'elosed through the line winding 46 of the line switch C. This circuit extends from ground G through springs 92 and 93, line 98, springs 99.'and

100, S and. 9, receiver 2, transmitter 1, line 101, springs 95 and 9-1, winding 46,, contact point 102 and armature 65 to batteryle'ad 1.05. .The \Yill(1lllg.46 attracts the armature 42, which forces spring 97 into contact with i 56 to the selector F, whereupon the rela 104 becomes energized over a circuit ing from ground G through the lowglgivinding of said relay, side switch wiper 77, 5 springs 56 and 5 5, thence over-line conductor 98 to and through substation A andihack over the other side of the line, through ,winding 68 ofthe meter magnet, springs 49 and 50, side switch wi r 76 and upper cuit from ground G. through springs 107 and 108 and relay 85' to battery lead 105.

The, relay '85, upon energizing, completes a 42 The line windin 46, by which the armntui'e 42 was attracts is deiinergized as soon as the armature 41 is attracted; by winding 43, but the armature 42 remains held up for an instent by the winding45, which is energized in series with the winding 43 and is then caused. to deiinergize slowly by being short-circuited through springs 111 and 112 circuit of winding 44 shall be closed before the circuit of winding 43 is broken.

When'the line switch C operates, eir Ic'uit is also closed throu h the winding 69 of the meter magnet. T is circuit extends from ground G through springs 109 and 110, 52 and 51, winding 69 and springs113 and 112 to battery lead 105. The current in ing in the winding 68, and the magnet 67 is not operated at this time.-

springs 53 and 54 by the plunger of the line switch C closes a circuit through the relay 66 is maintained energized until the wiper 29 passs oii the contact corresponding to the last successive busy trunk and breaks the y 6 circuit of relay1'14. After thereley'iifi dewinding of relay 104 to t e battery lead 105. The relay 104, uponenergizing', closesa' cirdigit, the im ulse s arated four times.

by the plunger arm. This insures that the ma' et 80 to The closure of contact between the hank gn rela 87 andside switch wiper 79 to G through magnet 58, interrupter springs neness energizes the master switch continues to op erate until the pin 64 registers with one the openings in the plate 62, whereupon he .arinature 65' falls back, breaking the circuit of the motor magnet 58 and locking'the plunger shaft, with the idle. lun r's standmg in front of an'idle trun f the next trunk after the one seized by the switch C is idle, the master switch will stop opposite this trunk, as indicated in the drawm s.

It will be assu'med'that the trunk ine-s which lead to the. jacks J are connected to the fourth level of the bank contacts of the selector F. I In order to obtain connection with one of these trunks, the calling sub- 30 scriber operates his calling dial for the digit 4. As the impulse wheel 10 returns to normal position after being rotated for this rings 3 and-Q-are separe separated. the relay 104 at the selector F. deiiner 'zes momentarily. Since the relay 1 *is s ow noting, it does not have time to de'e'nergize durin the momentary interruption of its circuit y relay 104; consequently,

, each time the relay 104 deiinergizes a circuit -is closed through the vertical magnet 74.

Thi's 'circuit extends from ground Gr through springs 107 and 118, 119 and 120, relay 86, vertical'm at 74nd side switch wiper 7 9 to better sad The vertical magnetreceives our impulses oyer this circuit and operates to raise theshaft four steps. The relay 86, which is included in circuit with the verticelma'gn'etfis energized by the first of these pulses, but, being slow acting, does notuse 'ze-until hfter the-last ima lse 's d live '.*;'=Wh'e th rel 86 this winding is opposed by the currentflow- 1 e n e W ener gizes, a circuitijisiclosed fromfground (l through 121.;and 122 and private ttery ,lead' 105." When the relay 86 deenergius the private, magnet in turn deiinergiz'es In 1 allows the side switch to ass toseoond-position.

' 7 he sidei switoh w1per79, in passing from 11.0 first to secondposition, disconnects the but tery from the ivertical magnet 74 and closes a circuit through the rotary magnet 75.,

-This circuit extends irom' ground Gr through interrupter spiings123, maggiet 7 5, 1 5

attcry lea 105. Since this circuit includes the interrupter springs 123,; the magnet 7 5 operates in a-xnanner similar to that of a buzzer to advance the wipersstepby step as long 20 a sfthe side switch remains in second posi tlon; -Whenthe rotary [magnet energizes,

its armature alaopresses down the armature of theflprivate magnet 80, which, when it falls back, causes the side switch to be 1.25

trip -to third position.v I-f'the first trunk of t e fourth level is idle, the side'switch is tripped to-third position as soon asthe shaft wipers have been 'mtated one step. If the firsttrunk; is husy however, thepriyete ts ach time these springs 35 wiper 72 finds the first private bank contact grounded, and forms a circuit extending through side switch wiper 78 and private magnet 80 to battery lead 105. The private magnet thus becomes energized and locks the side switch in second position, causing the rotary magnet to continue advai'icing the shaft wipers step by step until the private wiper 72 finds the non-grounded contact or an idle trunk, whereupon the prirate magnet 80 denergizes and the side switch passes to third-position. The movement of the side switch from second to third position breaks th .circuit of the rotary magnet 75, disconnects the line relay 104 from the line and extends the connection to the jack J through the condensers 124 and 125, and conductors 126 and 127. Also, at the instant the side switch of the selector passes to third position a circuit is closed from ground Gr through the upper winding of the trunk relay128, springs 129 and 130, shaft wiper 73, side switch wiper 7'7, thence to and through the substation A and back over the other side of the line, through side switch wiper 76, shaft wiper 71, relay springs 131 and 132 and lower winding of relay 128 to the battery lead 105. The relay 128, upon energizing, connects the relays and 134 with the trunk conductors 126 and 127 respectively, and provides a guarding ground potential for the selector private bank contacts of the seized trunk. This potential extends from ground Gr through springs 135 and 136 to said private bank contacts.

It will be remembered that the relay 87 ofthe selector F is included in the encrgizing circuit 0f.the rotary magnet 75. This relay, being slow acting, remains energized for a short time after the rotary magnet has dci nergized for the last time. At the instant the side switch passes to third position the selector private bank contacts of the trunk are provided with a guarding ground from ground G through springs 137 and 138 and wiper 72. This ground protects the trunk until the relay 128 has time to pull up. -The relay 87 dei nergizes after a short time and completes a holding circuit for relay 85, said circuit extending from ground G through springs 135 and 136, wiper 72 side switch wiper 78, springs 138 and 130 and relay 85 to battery. .This circuit is closed before. relay 85 has time/to fall back after its r'orn'iercircuit is broken by the dci ncrgization of relay 104 when the side switch passes from second position.

When the relay 13 i is connected to the trunk conductor 1 a circuit is closed from 7 ground G'" (Fig. 2) through relay 140, springs 141 and 1 :2. conductor 127, springs 143 and 14-1 and. velay 134 to battery lead 105. The relay 140 is energized over this circuit but, being of a comparatively high.

completes a circuit from ground G Fig. 1)

through relay 133, springs 147 and 14S, conductor 126, tip of jack J and plug P and ,impedance coil 149 to battery lead 105. The

relay 133, upon energizing, provides anew holding ground G, for the selector release relay 85, and connects itself with conductor 126 through its own springs 150 and 151, so that ltcannot he deenergized until the plug, P 1s removed from jack J.-

The engagementiof the sleeve conductors of the plug P and jack J completes a circuit from ground Gr through relays 152 and 153 to battery lead 105. The relay 153, upon energizing, breaks the circuit of relay 140, allowlng it to deenergize and extinguish lamp 145. The engagement of the ring springs of plug PT and jack J'completes a circuit from ground G through relay 154, said springs of plug P and jack, J, conductor 127, thence to and through" relay 134 to battery, as previously traced. ,The relay 134 is not operated over this circuit. The relay 154, however, attracts its armature and prevents the closure of the circuit of lamp 166 by relay 152.

After ascertaining the number of the del sired line the operator inserts the plug P into the jack J and operates key K to place springs 156 and 158 in engagement wit-h .springs 157 and 159, respectively, whereby line. is #2220, the operator now presses the button 88 twice for the first digit and then presses the button 89 once. Each time the button 88 is pressed a circuit is closed from ground G through springs 166 and 88, 157 and156, tip of plug P and jack J",

jtrunk conductor 160, vertical line relay-167 of selector I (Fig. 3) and upper winding of relay 168 to battery lead 176. The energization of relay 168 at this time is functionlcss. Each time relay 167 is energized a circuit is closed from ground G through springs 169 and 170, side switch wiper 171, contact point 172, springs 173 and 174 and vertical magnct 175 to battery lead 176. The vertical magnet receives two impulses overthis circuit and raises the wipers 177 178 and 179 permits the side switch'to pass from second position, whereby the vertical magnet is disconnected from the impuls'sprin'g 170, and a circuit is closed through the rotary 'inagnet 184. The rotary ni'agnet184 operates in the same manner as the rotary magnet- 75 of the selector F (-Figi'llto rotate the wipers onto an idle trunk line leading to a selector L, after which the side switch passes to third position. After the side switch has passed to third position, the seized trunk is rotect'edfrom seizure by any other selector by a guarding ground extending from ground G through side switch Wiper 185 and private wiper 179 to the selector private bank contacts of the said trunk. p

The operator now presses the button-88 V twice andbutton 89 once for the second digit Each timeIt-he button 88 is pressed a circuit is closed through the relays 167 and 168 of (the selector 1, as previously traced.

Sincethe side switch is now in third position,

the energization of relay"1'68- closes a cir-- cuit from ground G through side switch wiper 480, relays 4-81 and 188 in multile and springs 189 and 190 to battery lead 1 6. These relays are energized the. firsttime the button 88 is pressed and, beingslow acting, do not delinergize between impulses, but remain in their operated position until the last impulse is delivered. In its energized position, the relhy e81 dpens-jthe circuit through the selector and connects the impulsespring 170 with thee-vertical side of the trunk leading to the selector L. Thus each time the relay 167 energizes, a circuit is closed from ground G through springs 169 and 170, side switch wiper 1 191 and 192, side switch wiperlfltl springs 1 i and 195, wiper 177, side switch wiper 197 and vertical line relay 198 to battery -lead'176.,' The relay 198, upon energizing,

closes a circuit from ground G through springs 199 and 200, 201 and 202 and ertical magnet 203 to battery lead 176. The

vertical magnet receives two impulses over this, circuit and operates to raise the shaft Wipers two steps. \Vhen the button '80 is bythe'operator the relays 181 and,

er 16s,

ithe selector ifare energized over a v circuit "whiclthas been traced before. The 25 relay '181,.uponenergising, completes a ciI'-- ing and denergizing, causes (1, springs suit from ground Gr. through springs 160 and 479, side switch wipeiy186 (in third position), springs 20% and 205, 206 and'207; wiper 178, side'switch'wiper 208 and rotary relay 209 to battery lead.176. The relay 209,- upon energizing, completes a circuit from ground G throng-h springs 199 and 210 and private magnet 211 to the battery lead 176. The privatemagnet upon energizthe side switch to pass to second position, whereupon a, circuit is closed through the rotary magnet I 212. The rotary magnetthen operates in the manner explained for the rotory magnet of the selector F. to rotate the wipers onto the contacts of an idle trunk line leading to a connector M (Fig. 4). 1n the selector L the circuit over which the private magnet 211 is energized to lock the side switch in second position while the shaft wipers are being rotated over busy trunks extends from the guarded private bank con-j tacts of said trunks over the wiper 213, rc-

lay 214, side switch wiper 215 and magnet 211 to the battery lead 176. The relay 214! is not energized over the circuit on account of the comparatively high resistance of the magnet 211.

Sincethe relay 188 of the selector I is en- .ergized at the time the rotary line relay 181 is energized, a circuit is also closed from ground G: to and through the private magnet springs 206 and 207, asbefore traced, and thence through the springs 2'15 and 216 and the magnet 217 to the battery lead 17 6. -The' magnet 217, upon energizing. ro-

tates-the wheel 218 .one step. This wheel is so arranged that after it receives three such step the springs 219 and 220-engage each other.

'When the operator operates. her calling apparatus for the third digit 2 the selectorrepeater I operates in the manner just ex-' plained to repeat two impulses to the vertical side and one impulse to therotary side of the trunk with which ithas made connection. Since the side switch wipers 197 and 208 of the selector L are in third posi tion, these impulses pass through the shaft wipers 221 and 222. and the trunk conductors 223 and 224 to the connector M (Fig. 4). The two vertical impulses for this digit pass from the conductor 223 through the relay 225 and the upper Winding of the relay 226 to the battery lead 176. The relay operates in response to these impulses to transmit two impulses from ground G" tl 1rougli' the springs 228 and 227, 229 and 230, side switch wiper 231 and vertical mag-- net 282 to the battery lead 17 6. The'vertical magnet operates to raise the wipers of the selector two steps.

passes from conductor-224 through the ro- .tary line relay 233, lower winding of the rclay 226 and'spring's 23 i and 235 to battery.

The'rotary impulse for the third digit2- I The energization of the relay 233 closes a circuit from round (i throu h SH'lIW'S I sponse to the impulses for the last. digitd) in the manner just explained, except that,

since the digit called is 0, ten impulses-in 'stead of two are repeated over the yertical side of the trunk. The operatie'iisi the vertical relay 225 for these impulsescause the rotary magnet 238 to be energizedten times over a circuit which, with the exception of the magnet itself, is the same as that traced. for the vertical magnet 232. The rotary n'iagnet operates in response to these in'ipulses to rotate wipers of the con: nector ten steps onto the contact}. ,,of line #2220. The rotary impulse for" *this last digit operates the rotary relay 233, as for the previous digit, and causes the private magnet 237 to trip the side switch to third position. At the selector I the magnet 217 is energized once more by the last rotary impulse and rotates the wheel 218 one more step. This last step of the wheel 218 closes the contact between springs 219 and 220, whereby, as soon as the relay 188 denergizes, a circuit is completed from ground G through side switch wiper 185, relay 239, springs 272 and 271, 219 and 220 and interrupter to battery. The relay 239 is energized intermittently over this circuit and operates to open one side of the connection between the springs 194 and 195, and. to close a circuit from ground it through side switch wiper 480, springs 243 and 19 1, and thence over the heavy (Ollllltt'ifil'h' to and through the vertical rclay 225, and upper winding of relay 226 of the connector 'M. over a circuit which has previously been pointed out. Since the side. switch of the connector is now in third position, the cnergization of these relays completes a circuit from ground G through springs 228 and 227, 229 and 230, side switch wiper 231, ringer relay 245 and springs 246 and 247 to the battery lead 176. The

relay 2-l5. upon energizing, ,connccts thcgenerator Q, with the called line to ring the bells 248. Since the relay 239 at thc selector l is eiiergized intcrmittcntly, the ringer relay 245 of the connector M is cnergized intermittently also. 7 The first time the relay 2+5 dci ncrgizes after the called subscriber rcnioycs his receiver in response to the call, a circuit is closed from ground i at the connector through side switch wiper 219, lower winding of relay 250, ringer relay springs 251 and 252, side switch wiper shaft wiper 251, springs and 256, line 257. primary winding of induction coil 258, transmitter 259, springs 22 and 23, line 260, wiper 261, side switch wiper 262, upper winding of relay 250 and springs 263 and 217 to battery lead 176. The closure of this circuit furnishes the called substation with talking current and causes the relay 250 to be energized. The relay 250, upon energizing, shifts the spring 234 out of engagement with spring 235 and into contact with spring 264, whereby a circuit is closed from ground G through side switch wiper 249, springs 264 and 234, lower 'inding of relay 226, rotary relay 233, thence over the heavy conductors through the selector L (Fig. 3) to the selector repeater I, thence through sprin s 215 and y 265, relay 266, springs 267 an 192. side switch wiper 193, springs 195 and 191, wipers 177, 197 and 221, conductor 223 and relays 225 and 226 to battery. The relay 226 is not energized over the circuit just traced, because the current flows through its two windings in opposite directions. All the other relays included in this circuit are energized, the relays 225 and 233 of the connector M, however, having no function at this time. The relay 266 of the selector 1, upon energizing, shifts the connection of the rotary line relay 181 and lower winding of relay 168 from battery lead 176 toground at G and closes the circuit of relay 268. The relay 268, upon energizing, separates springs 271 and 272 and closes contact between sprin S 269 and 270. The separation of springs 2:1 and 272 opens the circuit of the relay 239 so as not to cause the called subscriber to be rung again after he has answered. The closure of springs 270 and 269 provides a locking circuit for relay 268 so that it will not dci ncrgize when the called subscriber hangs up his receiver and allowsthe relay 266 to deiinergize. This locking circuit extends from round G throu h side switch wi )er '185, springs 270 and 269 and relay 268 to battery. The. circuit which is closed through the relay 268 by relay 266 is the same as that just traced, except that it includes springs 273 and 274. instead of springs 269 and 270. v

The shifting of the spring 183 of relay 266 completes a circuit from groan. it through side switch wiper 185, springs 275 and 183, lower winding of relay 168. relay 181, trunk 161, ring conductors of jack 2 andplug P springs 158 and 276 (the key K is restored as soon as the operator completes the call), relay 277. springs 278 and 156, tipof plug P and jack J", conductor 160 and relays 167 and 168 to battery.

The relay 277 at the cord circuit 0 exover a circuit extendin tinguishes the lamp 27 to signify'to the op erator that the called subscriber has an (The lamp'279 is lighted as soon .are energized but without unction at this time.

When tlieoperator'isnotified that the called subscriber has answered by the extii'ig'uishment of 1amp279, the button 282 is pressed-to cause the calli'n subscribers meter -(Fig.' 1) to register. his is accomplished in the following manner: When the button 282 is pressed the relay 283 is connected in multiple-with the relay 154. This increases the current in the relay 134 (Fig. I

1)- suflicientlyto cause it to operate, and the relay 283 is operativelyenergized also. The relay 283, upon energizing, completes a circuit for itself from ground G through springs 528i and285, 287 and 286, relay 283 and thence througli plug P, trunk 127 and relay 134, as has been previously traced. The relay 283 thus remains locked in multiple with the relay 154 after the button 282 is released. The energization of therelay 134 (Fig. 1) ,transposes the connections between the windings of the relay 128' and the line conductors, and thereby reverses the current in the calling line. This reversal of current causes the winding 68 of the meter' magnet 67 to assist the winding 69 and therefore the armature 70 is attracted and registers the call on the in'eter E. When the armature 70 is attracted the winding 68 is short-cir-,

, .cuited by the springs 288 and 289, and the armature is held up by the winding 69'alone.

The line of the calling subscriber is pro.- tected from being seized by any other calling subscriber as soon as the line switch operates. This protection is furnished by a ground. potential which extends from ground G throuh the'springs 109 and 110 of the selector F, springs 52 and 51 and conductor 290 to the private bank contact of the substation A in the bank of each con nector which has access 'to that line. The

called line is. protected in a similar. manner as soon as the side switch of the connector M passes to third position, whereby a guarding ground potential extends from ground '6 through. the side switch wiper 249 and the private shaft wiper 291 to the private.

bankv contact 292,- and thence to the correspondingcontact in theibank ofea'ch connector which has accessto the line of the substation A. From the con-tact point 292 a circuit also extendsjthrou'gh the cut-oi? relay 293'to battery.' The relay 293; u'ponw energizing, disconnects the switch-N from the called line and completes connection between the contact upon whichwiper'25e is resting'and the line 257.

The manner in which the guarding potential at the private bank contacts pre vents a connector M from connecting with v a busy line is as follows: if there is a guarding ground potential on the connector private bank-contact of the, called line at the time the privatemagnet 237 is operated by the rotary relay .233 in res ones to the rotary impulse forithe last digit of the number of that line, an energizing circuit is closed from said guarded bankcontact through wiper 291, side switch wiper 2&9 (in second position), rivets magnet springs 295 and 296 and re ease magnet 537 to battery lead 176. -The magnet 537, u on venergising e,

causesthe, mechanism of. t e connectorte be restored tonormalposition, whereby its wipers are removed from contact with the called line. Now,'since the connector is in normal position, the ground impulses which are sent over the vertical side of the line by the selector repeater i for ringing the called substation do not operate theringing relay 245 of the connector, but operate the vertical magnet 232 instead, causing the switch shaft to he raised one or more steps. As soon as the she-this reisedthe first step the springs 297 and 298 are permitted to come into engagement, thereby connecting the busy signaling machine R with the calling line through said springs, side switch wiper 253, ringerrelaysprings 251 and 252, condenser 299, and thence over the heavy conductors shown in Figs. 4, 3, 2 and 1 to substation A. The return circuit is over the other side of the line and through relays 225 and 226 of the connector M to the battery lead 17 6 to which one terminal of the busy signaling machine It is con nected. The busy signaling current in this circuit produces-the usual busy buzz in the C receiver of the calling subscriber.

When the called subscriber hangs up his receiver upon the termination of a conversation, the connector back bridge relay 250 deenergizes. Therelays 225 and 233 of the connector and relay 266 'of the selector 1 which were energized by the operation of relay 250 thereupon deinergize. The den- ,ergization of the relay 266 breaks the circuit of the relays 167 and 181' of the selector I 'and relay 277' of the cord 0. The relay .277, upon denergizing, closes the circuit of lamp 279. 1

ion

When the calling subscriber hangs up his receiver, whether after'a conversation or after having received the busy signal, the

circuit ofrelay 128 (Fig. 1) is broken. The relay 128 the'reupon deiinergi'zes and breaks the circuitlo'f relay 13+ and of relays 283 and 154: at the cord 0. The relay liia'upou deenergizing, closes a circuitfrom ground G through springs 284 and 285,300 and 301 and lampl55. The simultaneous glowing of lamps 155 and 279 signifies to the operator that the connection may be taken downs l Vhen the plugs are remoyed from the jacks all the automatic switching apparatus employed in the connection is released. The removal of the plug P" from jack J breaks the circuit of the relay 133 (Fig. 1). The relay 133 thereupon deenergizes and breaks the holding circuit of the selector release relay, 85. The relay 85, upon deenergizing, closes a circuit from ground G through springs 107 and 118, 119 and 302, release magnet 81 and springs 81 and 83 to battery. The magnet 81, upon energizing, immediately restores the selector F to normal position. The dee nergiza-tion of the relay 85 also breaks the holding-circuit of the winding 41 of the line switch C, allowing it to be re-.

stored to normal position, and at the same time the circuit of the winding 69 of the meter magnet 67 is broken, allowing said' magnetto be restored also.

The removal of the plug P from the jack J by the operator causes the circuit of the relays 161 and 165 to be broken. The relay 16 1 deenergizes immediately, while the slow acting relay 1 0 holds its armature up for an instant. At theinstant the relay 161 denergizes, both trunk conductors 161 and 162 are grounded through thesprings of relay 165. The grounding of these conductors energizes the relays 167, 181 and 168 of the selectorrcpeater I. The cnergization of these relays grounds both sides of the trunk leading to the selector L over circuits which have already been pointed out, and the magnet 217 is also energized to rotate the wheel 21.8 one more step to allow springs219 and 220 to disengage. The energization of relays 167, 181 and 168 also closes a circuit from ground G 9 through springs 303 and 30:4, release magnet 305 and springs 189 and 190 to battery lead 176. The impulses which are transmitted to the trunk line'leadil'ig to the selector L by the simultaneous energization of the relays 167 and 181 of the selector I pass through said selector L and through therclavs 225, and 226 of the connector M. The simultaneous energization of these relays closes a circuit from ground (I at. selector L through side switch wiper 215, relay 214, wiper 213, conductor 53-1, springs am 636, releasemagnet- 537 and springs 216 and 247 to battery lead 176. The magnet 537, upon energizing, restores the shaft and side switch of the connector M to normal position. The energizing of the relay 21-1 of the selector L completes a circuit from ground G at the selector I through side switch wiper 185,

shaft wiper 179 and springs 538 and 539 and release magnet 540 to the battery lead 176.

The release magnets 5 10 and 305 of the switches L and 1, upon energizing, attract their armatures and hold them in readiness were energized as result'of the deenergization of the relay 161, whereupon the switches L and I are released. simultaneously.

1t having been explained how a two-wire substation A may obtain connection with a three-wire substation A, it will now be explained how a connection may be extended from the three-wiresubstation A to the twowire substation A. As the dial at the substation A' is rotated forward preparatory to calling the first digit after the receiver has been removed from. the hook, the rotary impulse spring 19 is momentarilyforced into contact with the ground-post 21, whereby a circuit is closed from ground G through the springs 306 and 307, springs 21 and '19, line conductor 257, springs 256, 308 and 309, trip magnet 310 to the battery lead 176. The trip magnet, upon energizing, releases the plunger, which'operates to extend a connection from the line of the substation A through the springs 311 and 312 and 313 and 311 and over the conductors 315 and 316 to the selector L (Fig. 5). The closure of contact between the bank springs 318 and 319 by the plunger of the line switch N completes a circuit from ground G through the said springs 318 and 319 and cut-off relay 293 to the battery lead 176-. The cut-ofi' relay 293 thereupon energizes and opens the bridge across the line conductors 260 and 257. The closure of contact between the bank springs 320 and 321 by the line switch plunger completes a circuit from ground G through the relay 322, common segment 323, wiper 324, contact point 325, springs 321 and 320, release magnct 326to battery lead 176. The relay 322 energized over this circuit, but

on account of its comparatively high resistance does not permit. sufficient current to flow to energize the release magnet 326. The

- relay corresponds to the relay 114: of the master switch D (Fig.1) and, upon energizing, causes the master switch D to operate 'in the same manner as explained for the through its line relays 328,

side'switch of the gosition, a circuit 45 341 and 342.

,5 the plug P and jack J tl irough the cut-off relay 354, which energi'zes and the ground post 21 thejcircuit is closed from ground G through the springs 306 and 307, 21 and 20, line 260,'bauk springs 311 and 312, trunk conductor 315, side switch 5 wiper 327' and vertical selector L" to the battery lead 176. The

grounding of the rotary impulse springpltl at the substation completes a circuit which extends over line'conductor 257 through 10 spiilliigs 31,3 and 314. trunk conductor 316,

side switch wiper 3:29 and rotary 'line relay 330 to the battery lead 176. The selector U is essentially the same as the selector L, Fig. 3, and operates in response to the impulses and 330 in the same manner as explained for the selector L to extend the connection over the trunk conductors 331, 332, through the condensers 333 and 33-1 to an idle jack J When the selector L reaches third through the relay 335, trunk conductor 332, selector wiper 336, side switch wiper 329, trunk conductor 316, line 257, thence 25 through the substation A. and back over line conductor 260. trunk conductor 315, side switc i wiper 327, shaftwiper 337 and relay 338 to the battery lead.'-

ie-relays'338 and 335 thereupon energize, 'tlie relayf338 op-- era-ting to close a circuit from round G through springs 339 and 340 anrf relays 341 and 3' tothe battery lead, '1 -he energizet-ion ofathe relays 341 and 342'is without any direct effect. The energizatibn of the relay 335 completes a circuit from} ground G through the upper winding of'relay 343,

sp'ririgsiSi-i and 345, conductor 346, contact point 347, armature 348, relay 349, arn1'ature 350, contact point 351 and lower. ,windingof 0 relay 343 to the battery lead. Therelay349 thereupon energizes and completes a circuit through the lamp The'relay 343 is also energized over the circuit just traced and connects the ground G with the relays I Upon seeing the signal of the lamp 3o, the operator inserts the plug P into the jack J thereby connecting the cord G with the line of the calling subscriber.

1e engagcn'ient of the sleeve conductors of completes a circuit disconnects the relay 349 from the trunk,,thereby allowing the lamp 352 to be extinguisheds lVhen the plug-is in-,

sertcd in the jack the supervisory relays 356 and 357 are vboth energized. The energizing circuit for the supervisory relay 357 extends from ground (it through' the said relay, ring conductorsof plugP and jack f no J thence through the lower Winding of, re

lay 33 to the battery lead. The energizing circuit for the relay battery lead 17 6 through the said relay, tip springs of plug P and jack J line relay 328 of- I, Fig. 6;

switch Wiper 360, lower jack J and is closed from ground ace and .369, 3 magnet 373and-sidc s'witch wiper 374 to 356 extends from the conductor 5 346, springs 345 and 344, thence through the upper windingof relay 343 to ground G Upon finding that the substation A of the two-wire exchange is wanted, the operator inserts the plug 1 into the ack J and operates the key K whereby the impulse springs 'QQ-and 91 of the operators calling device are, bridged across the trunk conductors 358 and359, which lead to the selector repeater When this occurs a circuit is closed from ground G Fig.6, through side winding of relay sleeve contact of plug P, springs 362 and 363, im also springs 91 and 90, key springs 364: and 36.5,. tip -conductors ofplug P and jack J trunk conductor 358 and upper Winding of relay 361 to battery lead 105. The relay 361, upon energizing, completes a circuit from ground Gr through the springs 366 and 367 and relay 368--to the battery 361, trunk conductor 359,

lead 105. The operator at the cord 0 now operates the calling device for the first digit of the number of the-substation A, which will be assumed toybe 220. The operation of'the calling device for the first digit 2 causes the impulse springs 90 and 91 to be momentarily. separated twice. Each time theg esprings are separated the relay 361 of theijselector. repeater I' de'energizes momentarily; kSince therelay; 36.8. is slow acting itdo'es not have time to-denergize during the momentary interruption of this circuit by the realy 361.- Consequently, the engagementof' springs 366 and 369 completesthe circuit from ground .G through springs 0. and 371, relay 372, vertical battery lead 105., Tihe 'rertical magnet 373 re'ceivestwoihnpulseso er this circuit and operateetoraise the shaft wipers 375, 376

- and 377'two stepsh 'FlIhe relay 372, which is included in. ;-the energizing circuit of the vertical magnet 37 3,-is energized by the first impulse, but being a slow acting relay, does not deener ize until afterthe last impulse hasbee'n elivered. In it'sfenergized position, the relay 372 closes a circuit from ground G position, aguarding potential is extended from ground G through side switch Wiper 37 2 deenergizes, and

, through springs 482 and 378 and private magnet 379 to the battery lead 105.

- therefore.

- retardation coil 2-}91. wiper 382. p1 ivate wiper 377, private bank contact. 3823. thence to the corresponding contact in thebanks o'l all selectors which have access tothe trunk line which has been seized by the selector 1'. When a connectiian is thus extended by wav of the selector 1 to the connector ll. at circuit is'comp'leted trom ground (1? at the connector through side i twitch wiper te -blowerwinding of relay 38 sprin s 383 and N3. contact point 397. wiper 37w springs 39.) and 388 relay 390, 375. contact point 392, springs 39 -3 and 394 and upper winding of relay 39+ to the battery lead 105. -The relav 2394. upon energizing, completes a circuit through the relay 395 in the same manner in which-a circuit was completed through'the relay 3GB of the Selector The energization of the relay 390 of the selector 1 connects the ground G with the lower winding of relay 361. to take the place of ground G which is disconnected when the side switch passes to third position. Each time the relay 3G1 otthe selector 1" deenergizes in response to the impulses tor the second digit 2. the separation of the springs 388 and 389 breaks the circuit of the "ue relay 384 of the connector M. The relay of the connector. being slow acting. does not deenergize during the momentary inter-- ruption ot the circuit by the relay 384. and, ach time relay 384 deenergizes a circuit is closed from ground G through springs 396 and 397. 398 and 399, relay -tOO. vertical magnet 401, side switch wiper 402. to battery lead 105. The vertical magnet 401 receives two impulses over this circuit and ope ates to raise the wipers of the connector two steps. The relay 400, which is included in the energizing circuit of the vertical magnet 401. is energized by the first impulse. and completes :icircuit. from ground G through springs 484 and 403 and private inagnet 404 to thebattery lead 105.

livered to the vertical magnet.

The relay 400 being slow acting. remains en-' ergized until after the last impulse is delVhen it deenergizes it breaks the. circuit of the private magnet 404, which then allows the side switch to pass to second position, Each time the relay 2-361 of the selector 1 deenergizes to repeat an impulse to the line relay BS I ot the connector M. closed from ground G througlrsprings 366 and 369, 370 and 371 relay 372, relay d0?) and side switch wiper 374 to battery lead 105. The operation ot'the relay 372 at this time is tunctionless. The relay 405 is encrgizcd by the first impulse for the digit and. being slow acting. does not deenergize until after the last impulse is delivered. In its energized position the relay t05'short circuits the relay 390 and the retardation coil 391 throughthe springs +00 and thereby removing the resistance of said relay times and operates in only remaining a circuit i not permit sufiicient.

and retardation coil from the circuit of the connector line relay 384 while'it is operating. in its energized position-the relay 405 also connects the ground G with the lower, winding of relay 361 to take the place of ground G, which is disconnected by the 'deenergization ot' the relay 390 when it 1s short circuited. \Yhen the operatous calling device is operated tor the last digit 0 the line relay 361 of the selector repeater l is deenergized ten the same manner as xplained for the previous digit to repeat ten impulses to the line relay BS-t-ot the onnector M. Each time the relay 38+ deenergizcs in response to this last series of impulses. a cir uit is closed from ground tl through springs 396 and 391-398 and 390; relay 400, springs 408 and 409, rotary magnet 5+1 and side switch wiper 102 to the battery lead .105. The rotary magnet thus receives ten impulses and operates to rotate the wipers 01" the connector ten steps onto the contacts of the desired line The relay u'lt) operates in the same manner as explained for the previous digit to maintain the circuit of the private magnet tot closed during the time the il'npulses are being delivered through the rotary magnet 541. After the last impulse is delivered, the private magnet tO-t deenergizes, if the called line is idle. and allows the side switch to pass to third position, whereby the connection is extended to the called line. \Vhen the side switch wiper 183 of the con- 100 nector passes from secondto third position the ground G is disconnected from the lower winding of relay 384- and said winding is connected to ground G through the relay 410. The relay =t10 is therefore in 105 cluded in the circuit of the relay 390 of the selector 1' and is'ot sutiiciently high resistance to reduce the current in the relay 390 enough to allow its armature to tailback.

\Vhen the armature ot' the relay.39() falls 0 back, the ground ti is disconnected from the lower winding of the relay 361 and the ground.connection for this winding is through relay 4:11 to ground G. After the operator at the cord t) has operated the calling device for the last digit, the key K is restored. to normal-position, whereby the calling device is disconnected from the cord and the supervisory relay +12, and impedance coil 413 are substituted. The relay -l12 is therefore included in circuit in series with the line relay 361 of the selector'l andrelay 411. The relay'tll, being of comparatively high resistance, does current to flow through 25 the, relay 412 of the cord circuit to cause it to attract its armature, and therefore the lamp 414 remains lighted by a circuit which This circuit extends I called line is opened, and the ringer gem i asathe ringer relayf420 denei'gize switch wiper 432,

erator Q is bridged across the line of the called subscriber. Ringing current then vflows from one terminal of the generator Q through ringer relay springs 423 and,

424, wiper 425, conductor 426, springs 96 and 95 of line switch C, Fig. 1, line conductor 101, thence throughlthe bell to substation A and back over line 98, conductor 4-27, shaft wiper 428, side switch wiper 429, 'ringerrelay springs 430 and 431 to the otherterminal of the generator Q. The circuit. for this ringing current includes the springs 95, and 96 of the line switch C, Fig. 1 These springs are closed by the energization of the winding 44 as soon as the side switch of the connector M' reaches thirdv position. The circuit ofwinding 44,-lext'emls from ground G? to side switch-wiper m'ofithe eonnector, private Wiper 433,]corit'act "456; conductor 290 and winding .44 {:tqth'c b'atf-- terylead 105. When the calledsubscriber removes the receiver,- or as soon thereafter cuit ISClOSSCl from ground Gifithibug switch wiper 432' of thefconnector," ar winding of back bridge relay 435,"ringerj relay springs 436' and 430,- thence through the substation A, through the talking cir-v cuit, back to the connector M over the cohor side of the line, through ringer relay springs; 424 and 437, private magnet springs 438 a id 439, upper winding of relay 435 and side switch wiper 402 to the battery lead 1951 The relay 435, upon energizing, shortcircuits'thehigh resistance relay 410 and closes the circuit of the relay 440, which circuit extends from ground Gr through side Y relay 440 and springs 441 and 442 to battery lead 105. The relay 440,

upon energizing, opens the circuit of the ringer relay 420, reverses the connections between the windings of relay 384 and the 1 line conductors and also completes the locking circuit for itself through the springs 443 and 422, which circuit is independent of the springs 441- and 442 of the back bridge relay 435.

This transposing of the connections the windings, of the relay f 384 reverses the current through the relay 390 which is bridged across the line to the selector 1, but this reversal of the chrrent,"

however, is without elfect. The short-cir- .cuiting of the high resistance relay 410 at .the connector by the engagement ot the springs 444 and 445 of the back bridge relay 435, however, increases the current through the relay 390 of the selector 1 sufficiently to cause it to attract its armature. The attraction of the'armature of the relay 390 connects the ground G to the lower winding of the relay 361 without interposed resistance, and therefore decuit of the lamp 414is broken, which signifies to the operator that the called su'bscriber has answered. a y

Whcnthe calling and called subscrihers hang lip-their receivers upon the termination of the conversation, the operator at the cord 0 is given the usual disconnect sigmi in the following manner :The hanging up of the "receiver at the calling substation A breaks the energizing circuit of the relays 338 and 335, Fig. 5. upon denergizing, breaks the circuit of the supervisory relay 356 of the cord 0, which relay thereupon'deenergizes and closes the circuit of the lamp' Azfi. When the receiver at the called substati'onA is restored, the circuit of the back bridge, relay 435 is broken. This relay, upon deenergi'aing, rernovesj the short circuit from the high resistance relay410,--which is thus again included in the circuit ofth'e relay 390 of the Selector I'.;-.. The relay 390 vthereupon deenergizes sufiici'ently to allow its armature to drop back and remove the short-circuit.

causes the relay 412 of the c rd 0' to deenergize sufficientlyto allow its armature drop back and from the relay 411. This close a circuit through the lamp 414. The

The relay 335, v

simultaneous glowing of the lamps 4l4'and 446Qindicates to the operator that both subscribers have b gee their receivers and that theconnection'hiay be released. The

automatic switches employed in the ,connection are released by the removal of the plugs P and P from the jacks J and J in the-following manner: When the plug 7 P is removed from the jack J the energizing circuit of the relay 343 'is broken.

Since the relay 338 is already denergized, the denergization of the relay 343 breaks the energizing circuitof the relays 341 and 342. The relay 342, being quick acting, deenergizes-immediately and. completes a cl1'- cu'it from ground G at I the selector L through side switch .wiper 447, relay 448, private wiper 449, springs 45 0 and 451, 452 and 453 and resistance 454 to battery lead 176. The relay 448, upon energizing, completes a circuit from ground G through the springs and 455 and release magnet 543 to the battery lead 176. The release magnet thereupon attracts its armature and holds it in readiness to release the selector L, and also completesa circuit from ground (i to the contact'point 456, armature 457, conductor 317,'springs 321 and. 320 (Fig. 4) and release magnet 326 to the battery lead 176.

The release magnet 326 thereupon attracts its armature and holds it in readiness to release the line switch N. The relay 341 (Fig. 5), being a slow relay, de'elnergizes shortly after the relay 342 and opens the circuit through the relay 448 of the selector L. This relay, upon' denergizing, opens the circuit through the release magnet 543'. When the release magnet 543 deen ergizes, it a'eleases the selector L and breaks the circuit 'of the release magnet 326 of the line switch N (Fig. 4), which de'e'nergizes and allows the plunger to be restored to normal position.

When the plug P is removed from the jack J the circuit of the line relay 361 of the selector 1 is broken. This relay upon deenergizing,

l breaks the circuit of the relay 368 and of the line relay 384 of the connector M. The relay 368,- upon deenergizing', completes the circuit for the release magnet 458. This circuit extends from ground G through the springs 366 and 369, 370 and 460, magnet 458, and springs 461 and 462 to the battery lead 105. The magnet 458, upon energizing, causes themechanism of the selector 1' to be restored to normal position immediately, and when the shaft reaches its lowest positic i the springs 461 and 462 are separated and the magnet 458 allowed to dcenergize. When the line relay of the connector M denergizes it breaks the circuit of theslow acting relay 395, which in turn deenergizes and closes the circuit of the release magnet 463. This circuit extends from ground Gd through the springs 306 and 397, 398 and 464, magnet 463 and springs 465 and 466 to the battery lead 105. The magnet 463, upon energizing, restores the connector M to normal position, Where upon the springs 465 and 466 are separated and the release magnet allowed to again deenergize.

In the foregoing it has been explained how the connector Mcomplctes connection with an idle line. If the called line is busy, how

ever, at the time the wipers of the connector are brought into engagement with the contacts thereof, the'connector will not complete the connection and the calling subscriber will be given the busy signal in the following manner: If the line of substation Av is busy the private wiper 4.33 of the connector finds a guardin ground on the pri' rate bank contact 466. This being the case, when the private magnet relay 400 de- 'rnmgizes, after the last impulse has been delivered to the rotary magnet 541, the circuit is closed from said guarded contact point 466 to the wiper 433, side switch wiper 432 (in second position), springs 467 and 468, relay 469, springs 470 and 403 and private magnet 404 to battery lead 105. As the relay 400 deenergizegthe sprin 403 engages the spring 470 before it disengages spring 484, so that'the latter circuit through the private magnet 404 is closed before its former circuit is broken. Thus the private magnet 404' remains energized, locking the side switch in second position and at the same time the relay 469 is energized. The relay 469, upon energizing, disconnects the rotary magnet 541 from the impulse spring 397,

transfers the holding ground of the private magnet 404 from the guarded private bank contacts to ground G which is connected to springs 471 through springs 472 and 473 and side switch wiper 474, and closes a busy signaling circuit from the busy signaling machine R to the calling line.- The circuit over which the busy signaling current flows extends from one terminal of the busy signaling machine B through the springs 475 and 47 contact point 477, side switch wiper 429, ringer, relay.

springs 430 and 436, condenser 478, thence over the heavy conductors through the switch I, cord 0, selector L, thence through the substation A and back over the other side of the line to and throughthe upper winding of the line relay 384 of the connector to the battery lead 105, thenceto the other terminal of the busy signaling machine. The busy signaling current flowing over this circuit produces a buzz in the receiver of the calling subscriber, which signifies that the called line is busy, and he thereupon hangs up the recelver and gives the'operatorthe disconnect signal.

It has been explained'how subscribers of either exchange mayobtain connection with subscribers of the other exchange through the medium of anoperator. Referring to Fig. 1, it will be evident that, besides having access to trunk lines leading to jacks J,

the selector F may also have access to trunk linesleading to connectors M, Fig. 6, where by subscriber A may obtain connection with any subscriber in his own exchange'without requiring the services of an operator.- Like-- 

